The invention concerns a process for producing (spinning) filaments made, e.g., from polyester, polyamide (polycondensate) or polypropylene. Devices appropriate to the process are also proposed.
For reasons of efficiency, increasing the delivery speed of filaments formed by pressing a melt through a spinning nozzle is a constantly sought objective. The magnitude of this "delivery speed" is not an absolute value that can be applied to every spinning process. Rather, it depends on the yarn which is to be spun. There is a fundamental distinction, for example, between technical and textile yarns, and textile yarns themselves are now being spun as either POY (partially oriented yarn) or FDY (Fully Drawn Yarn).
The pursuit of higher delivery speeds is currently limited by known effects of the delivery speed, these effects resulting mainly from changes in the morphology of the polymer from which the filament is formed. These changes, for example, reduce the strength or stretch of the yarn so that it is no longer suitable for its intended purpose. This also applies, indirectly, to cases in which the process ceases to be controllable at higher speeds, resulting in uncontrollable changes (and consequently non-uniform yarn characteristics) and/or yarn breakages (running problems).
1. Object of the Invention
The object of this invention is to achieve increased delivery speed while maintaining the same yarn characteristics and/or improved yarn characteristics while maintaining the same speed.
2. Prior Art
It has been known in the art for at least twenty years that, at higher delivery speeds, the frictional forces between the yarn and its accompanying or contiguous air layer can affect the yarn characteristics that can be achieved (U.S. Pat. No. 4,049,763). At the same time, it has been proposed to prevent these frictional forces by generation of an "assisted" accompanying air current to restore the positive characteristics of the slow process (U.S. Pat. No. 4,185,062 and U.S. Pat. No. 4,202,855). The proposed solution--an accompanying air current--had been proposed a long time previously, but for other reasons (U.S. Pat. No. 2,252,684). The term "assisted accompanying air current" here denotes the effect of special devices which generate an accompanying air current which is distinguished from an accompanying air current which is produced in any case as a result of entrainment with the yarn as the latter passes through the air. The above proposals all provided for the generation of the assisted air current following solidification of the yarn.
At the same time, it was proposed to subject the yarn to a tensile force before it had become solidified (U.S. Pat. No. 3,706,826). This tensile force can be generated by an air current. A similar proposal appears again somewhat later in U.S. Pat. No. 4,49 6,505 (=EP56 963), in which the air current is generated by an aspirator, following passage of the yarn through a heating zone adjoining the spinning nozzle. The heating zone is not included in WO 90/02222, in which the aspirator is connected to the spinning nozzle through a "spinning chamber".
Related or modified proposals have subsequently been put forward; for example, the proposal whereby, following passage through the spinning nozzle, the yarn passes through a shaft in which a predefined pressure is maintained (U.S. Pat. No. 4,702,871; 4,863,662 and U.S. Pat. No. 4,973,236). Special sealing devices are required to maintain the pressure within the shaft. This problem is circumvented in U.S. Pat. No. 5,034,183 and U.S. Pat. No. 5,141,700 (=EP-244217) in that the air (after it has been used for maintaining a predefined pressure) is discharged from the shaft at an increased speed.
The objectives of these latter proposals are not made clear. All are obviously intended to produce advantageous effects of one type or another. The patent specifications mentioned do not state whether phenomena other than empirically determined phenomena are involved. In some cases, the descriptions indicate the objective of selective application of a tensile force to the yarn close to the spinning nozzle.
For reasons of completeness, reference is made here to devices used for delivering yarns in the formation of non-woven products (e.g. U.S. Pat. No. 3,707,593). These devices are not relevant to the present invention, for reasons already stated in EP 244217 and not repeated here.